The invention relates to a device for use in the external fixation of parts of broken bones. More particularly, the invention relates to an improved external fixation device that has positively locking joints and permits two or more rotational degrees of freedom to be detachably locked using a single component.
A number of devices for use in the external fixation of bones are already known. One such device is disclosed in EP 0 011 258 A1 to ORTHOFIX, and includes an elongated middle body with two parts which are mutually displaceable along the body""s longitudinal axis. Each of the parts of the middle body support a clamping unit for use in the insertion of nails or bone screws into a bone segment, and a push/pull device acts on both parts of the middle body. The clamps rest by means of universal joints, i.e. ball joints, on the outer ends of the displaceable parts of the middle body and thus permit the nails or screws that are insertable into the bone segments to pivot in three dimensions. This device has the drawback, however, that the clamps are only frictionally fixed in place, and as a result the slippage-resistance of the apparatus once fixed in place is substantially reduced.
Another device for the external fixation of bones using pins is disclosed in U.S. Pat. No. 5,160,335 to Wagenknecht. The affixation bar is optionally telescopable and fitted with clamps that hold bone the pins in place. Brackets are used to attach the clamping elements supporting the connecting parts to the fixation rod. The connecting parts permit three-way rotation of the clamping elements relative to the brackets. The device includes connecting components and clamps used in fastening the bone pins, as well as connecting components with curved support surfaces to affix the clamp elements of the clamps to the connecting components on the affixation bar. The connecting components are designed in such manner that the clamp elements can pivot in three degrees of freedom relative to the clamps. This device has the drawback that the pivot joints can only be affixed relative to one another in frictional manner, and furthermore three screws must be tightened to lock the clamp elements in place.
There exists a need for an improved external fixation device to confer a palliative effect. In particular, there exists a need for an improved external fixation device that enables affixation of the joints in geometrically locking, hereafter positively locking manner, and furthermore allows two or more rotational degrees of freedom to be detachably locked using a single tightening screw. The present invention provides an improved external fixation device that is capable of providing these improvements.
The present invention is related to an external bone fixation system for clamping bone pins and a connecting element. The system includes a jaw having top and bottom surfaces, and an upper element having top and bottom surfaces, with the jaw and upper element being configured and dimensioned for retaining bone pins therebetween. The system also includes a middle element having top and bottom surfaces, and a lower element having top and bottom surfaces. The elements are disposed about a common axis. The upper element can swivel relative to the middle element about a swivelling axis transverse to the common axis, and the bottom surface of the upper element is clampable against the top surface of the middle element. The lower element can rotate relative to the middle element about the common axis and the bottom surface of the middle element is clampable against the top surface of the lower element. The lower element has a borehole extending therethrough, and is demountably attachable to and rotatable about the connecting element. Opposing surfaces of at least two of the elements are positively engageable, and the upper, middle, and lower elements are coupled by a common fastener disposed along the common axis. The jaw and upper element are coupled by at least one fastener that is not disposed on the common axis.
In one embodiment, the common axis is disposed substantially perpendicular to the swivelling axis, and the borehole in the lower element is disposed transversely to the common axis. The top and bottom surfaces of the middle element are substantially parallel. The common fastener that couples the upper, middle, and lower elements also releasably fixes the lower element to the connecting element. In addition, the middle element includes a recessed portion with an insert seated therein, and the fastener threadably engages at least one of the insert and the lower element. The bottom surface of the upper element is curved and is received in a recess in the top surface of the middle element.
The bottom surface of the upper element and the recess in the top surface of the middle element include mutually positively locking serrations which lock the upper and middle elements in any one of a plurality of swivelled positions. Furthermore, the top surface of the lower element and the bottom surface of the middle element include mutually positively locking serrations which lock the lower and middle elements in any one of a plurality of rotational positions. The serrations can be radially disposed about the common axis. The lower element includes a fastener for demountably attaching that element to the connecting element. The borehole of the lower element is disposed about a central borehole axis that is offset from and transverse to the common axis.
The lower element can have a fastener hole that is aligned with the common axis and includes threads for engaging the threads of the common fastener. The upper element also can have a fastener hole aligned with the common axis which includes threads for engaging the threads of the common fastener. A single fastener can arrest two or three degrees of freedom. The fastener can be configured and dimensioned to be engaged at either of a first end and a second end and to permit screwing action thereof.